1. The existing infrared remote control of encoding format includes two methods: PWM (pulse width modulation) and PPM (pulse position modulation).
Representatives of the two forms of coding are NEC and PHILIPS RC-5, RC-6 and future RC-7.
PWM (Pulse Width Modulation): Represents "0" and "1" with the duty cycle of the infrared carrier wave. In order to save energy, under normal circumstances, the time to transmit the infrared carrier wave is fixed, and the duty cycle is changed by changing the time when the carrier wave is not transmitted. For example, the commonly used TV remote control uses NEC upd6121, whose "0" is carrier transmission 0.56ms, not transmitting 0.56ms; its "1" is carrier transmission 0.56ms, not transmitting 1.68ms; In addition, for the convenience of decoding, Pilot code, the pilot code of upd6121 is 9ms for carrier transmission, and 4.5ms is not transmitted. The total code length of upd6121 is 108ms.
But this is not the case for all encoders. For example, TOSHIBA's TC9012 has a pilot code of 4.5ms for carrier transmission and 4.5ms for non-transmission. Its "0" is 0.52ms for carrier transmission and 0.52ms for non-transmission. The carrier transmits 0.52ms and does not transmit 1.04ms.
PPM (Pulse Position Modulation): The position of the transmitting carrier represents "0" and "1". From transmitting carrier to not transmitting carrier is "0", from not transmitting carrier to transmitting carrier is "1". The time for transmitting the carrier and not transmitting the carrier is the same, both are 0.68ms, that is, the time for each bit is fixed.
Through the above analysis of the coding, it can be concluded that "0" and "1" in a fixed format to learn infrared is very likely to be unsuccessful. That is, the 64-bit and 128-bit learning that is advertised on the market must be unreliable.
In addition, since the condition of air conditioners is far more than that of TVs, audio and video, and there is no standard, each manufacturer makes one according to its own format, resulting in even greater differences. For example: Midea's remote control uses PWM coding, the code length is about 120ms; Shinco's remote control also uses PWM coding, the code length is about 500ms. Such a big difference, if the concept of "bit" is used, how many digits should it be? 64? 128? Obviously, it is impossible to include such codes of different lengths.
2. The learning mode is now used to learn infrared CPU, nothing more than the following:
CPUs of MCS-51 series, microchip pic16 series, winbond w741 series, holtek ht48 series and above are widely used in remote controllers due to their low price and large usage.
The basic point of the above CPU is: the execution speed is about 1us, and the data memory is generally 256 bytes. If you learn in a fixed format, you can generally learn 128 bits (other programs will occupy some data storage); if you do not follow a fixed format, you need to find the smallest common divisor of the encoding as the basic unit, the number of bits that can be learned is greatly reduced , Can not achieve practical results. However, even so, the smallest common divisor found cannot satisfy all infrared devices unless the minimum unit is 26us (1000000 / 38k). If you reach this speed, the speed of the above CPU is far from enough, and due to the increase in storage, the data storage is also far from enough.
For TVs, stereos, etc., special remote control chips are generally used, such as nec, philips, toshiba, sanyo, mitsubish, and panasonic chips. The coding format is fixed, and there is only one code for one key, making learning easier.
The air conditioners are different, and each air conditioner manufacturer uses its CPU as a remote control chip according to its own requirements, and there are many encoding forms. For example, there may be no boot code (all TV audio products), and the checksum is cumulative (the TV audio products generally take the reverse code). Because there are many states of air conditioners, they must be sent at one time. There are cooling, temperature, wind speed, automatic, timing, humidification, heating, etc., so the code is very long, and the same button, the code sent in different states is different, causing learning Difficulties.
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